Developer skill sets vary a lot. I know my way around linux, but I'm no system administrator. So there's a good chance that I'll do something wrong if I built products using pure EC2. Also, frankly, I hate dealing with system administration stuff. I'll take a more expensive Aurora instance over a self-managed MySQL cluster any day of the week.
I'm sure there are tons of developers out there who know a lot about infrastructure and system administration. For those people, it might be worth spending time managing infra, but my time is absolutely better spent using a turn key solution and focusing on product development.
For smaller teams, getting feature-rich products out the door can be more important than building the most cost-optimal product. Bigger teams can afford dedicated staff to optimize infra.
I'm sure there are tons of developers out there who know a lot about infrastructure and system administration. For those people, it might be worth spending time managing infra, but my time is absolutely better spent using a turn key solution and focusing on product development.
For smaller teams, getting feature-rich products out the door can be more important than building the most cost-optimal product. Bigger teams can afford dedicated staff to optimize infra.